The present invention relates to improvements in apparatus for classifying the constituents of a stream or flow of randomly intermixed particles, and more particularly to improvements in apparatus of the type wherein the classifying or segregating stage is preceded by a reduction of the thickness or height of the stream or flow to thus facilitate access to those (undesirable) particles which are to be segregated from other particles. Still more particularly, the invention relates to improvements in that part or in those parts of the above outlined apparatus which serves or serve to convert a flow or stream of randomly intermixed (acceptable) first and (undesirable) second particles jointly forming two or more superimposed layers or strata into a second flow or stream wherein the number of layers is less than in the original stream.
It is well known and readily comprehensible that the removal of impurities and/or other particles from a thin layer, and especially from a single layer, of randomly intermixed useful and foreign particles is simplified and rendered more reliable if a moving flow or stream of intermixed useful and foreign particles is first converted into a single layer which is thereupon moved past suitable scanning or monitoring and ejecting or segregating (e.g., pneumatic ejecting) instrumentalities.
In the following passages of this specification, the term "first flow" will denote a flow or stream having a number of layers exceeding that number which is considered sufficently low to guarantee reliable detection and subsequent segregation of all undesirable particles (such as foreign particles and impurities). For example, a first flow of particles of comminuted tobacco leaves can contain highly satisfactory tobacco shreds constituting elongated comminuted tobacco leaf laminae as well as less desirable material including fragments of tobacco stem or tobacco ribs, so-called birds' eyes, pieces of rock and/or others. A "second flow" can contain the same constituents as the first flow except that it contains a single layer or a number of layers sufficiently low to permit reliable detection of foreign particles and impurities by optical, magnetic and/or other suitable means. The rod-like filler of a plain cigarette is considered to be of inferior quality if it contains a relatively high percentage of foreign particles and/or impurities. Moreover, relatively hard particles of tobacco stem, tobacco ribs, metallic fragments or the like are apt to puncture the tubular wrapper for the rod-like filler of a plain cigarette.
A particle flow of relatively low density is interpreted as constituting a flow of tobacco particles, as well as other commodities (such as for example foodstuffs), having a specific weight which is relatively low in comparison with the resistance it offers to the flow of air. Typical examples of such particles are tobacco leaf laminae and spinach; such particles and their fragments, as well as fragments of other sheet- or panel-shaped products encompassing, among others, fragments of salad as well as tobacco leaves--in contrast to stems or stem-shaped constituents of various vegetable products including tobacco stems, green beans as well as bundle- and bush-shaped gatherings of certain products including among others fresh thymian--can also be manipulated in the apparatus of the present invention.
All of the above-enumerated products, especially foodstuffs, exhibit the common characteristic that they must be cleaned, or inspected for the purpose of ascertaining the extent of their cleanness, with a very high degree of precision. Though not a foodstuff, tobacco can be said to belong to) the same category because it must be cleaned with a very high degree of precision and must be maintained in a state of absolute cleanness all the way to completion of its processing regardless of whether the final product is any one of various rod-shaped commodities including plain cigarettes, filter cigarettes, cigarillos, cigars or the like, or any other rod-shaped products. On the other hand, tobacco leaves often carry substantial quantities of impurities of a variety of sizes and shapes which strongly adhere to the constituents of rod-shaped smokers' products and/or are intimately admixed thereto. Moreover, it is advisable to segregate such foreign particles from useful constituents of tobacco leaves as expeditiously as possible because the foreign particles can interfere with predictable and/or optimal processing of tobacco. It has been found that tobacco leaf laminae (i.e., tobacco leaves devoid of rib and stem) are particularly likely to be processed with similar commodities of equal size and/or shape which are not desirable in smokers' products and, therefore, the laminae should be segregated from such undesirable foreign particles if the quality of tobacco products is to be kept at a desired level.
Commonly owned U.S. Pat. No. 5,558,199 granted Sep. 24, 1996 to Friedmann ROETHER et al. for "APPARATUS FOR FORMING A LAYER OF TOBACCO PARTICLES" discloses a highly satisfactory proposal to convert a continuously supplied multiple-layer first flow of particulate material containing randomly intermixed useful and foreign particles (such as fragments of desirable tobacco leaf laminae and fragments of randomly distributed impurities and/or fragments of tobacco ribs, stalks, eyes and the like) into a second flow containing only desirable particles. This is accomplished in that the number of layers in the first flow is reliably reduced to a number (e.g., one) which is sufficiently low to guarantee that the foreign particles can be readily detected and segregated from the useful particles. Moreover, detection and segregation of foreign particles can be carried out by employing a relatively simple but highly reliable apparatus.